The present invention relates to aqueous dye solutions of red disazo dyes, processes for their preparation and their use for dyeing paper.
The use of concentrated aqueous solutions of dyes has gained importance in recent years, in particular because of the advantages such solutions have over dyes in powder form. By using solutions, the difficulties associated with dust formation are avoided and the users are freed from the time-consuming and often difficult dissolving of the dye powder in water. The use of concentrated solutions has furthermore been stimulated by the development of continuous dyeing processes for paper, since in these processes it is advantageous to introduce the solution directly into the hollander or to add it at any other suitable point in the papermaking.
For some dyes, for example the dyes of the formula (1) defined below, formulation of concentrated dye solutions in free acid form presents difficulties, however, since deposits occur in the concentrated solutions during storage, especially at temperatures below room temperature, and these deposits cannot be dissolved again at all or can be dissolved only with an additional expenditure of work. Furthermore, concentrated solutions which are suitable as a commercial form should give clear solutions comprising about 1 to 3% by weight of dye, without a precipitate, when diluted for preparation of the dyebath, and this should also apply in the widest possible pH range.
Concentrated aqueous dye solutions in free acid form of certain dyes of the formula (1) defined below are known. However these solutions additionally contain considerable amounts of 3-chloro-2-hydroxypropyl trimethylammonium chloride or diethylene glycol monobutyl ether, both of which are undesirable.
The present invention was based on the object of providing suitable concentrated solutions in free acid form for the dyes of the formula (1) defined below which do not contain either a quaternary ammonium halide or a glycol- or diglycol ether. It has now been found that the dye solutions described below meet the requirements imposed in an outstanding manner. The present invention therefore relates to A) concentrated aqueous dye solutions comprising
a) at least 5% by weight, based on the weight of the solution, of a red dye of the formula 
in which
R and R1 independently of one another are each hydrogen, Cl, methyl or methoxy,
R2 and R3 independently of one another are each hydrogen, methyl or methoxy,
R4 and R5 independently of one another are each hydrogen or C1-C4alkyl,
A is an unbranched or branched alkylene radical, which can be interrupted by O, and
R6 and R7 independently of one another are each hydrogen or C1-C6alkyl, or in which
R6 and R7, together with the N atom bonded to them, form a substituted or unsubstituted 5-, 6-or 7-membered ring, which can contain further heteroatoms,
b) formic acid or a C1-C4alkylcarboxylic acid,
c) a solubilizing agent,
d) water and, if appropriate,
e) further additives, or
B) concentrated aqueous dye solutions comprising
a) at least 5% by weight, based on the weight of the solution, of a red dye of the formula (1),
b) formic acid or a C1-C4alkylcarboxylic acid,
c) water and, if appropriate,
d) further additives, with the condition that the solutions comprise no solubilizing agent and
less than 0.1% by weight of alkali metal halide, based on the total weight of the solution.
The present invention preferably relates to the dye solutions of group A).
In the dyes of the formula (1), R and R1 are preferably each H, methyl or methoxy, H being particularly preferred.
R2 and R3 are preferably each H.
R4 and R5 are preferably each methyl or, in particular, hydrogen.
Radicals A are, in particular, C2-C6alkylene radicals, in which the alkylene chain is straight or branched or can also be interrupted by bridge members, for example xe2x80x94Oxe2x80x94, or in which the alkylene chain is substituted, for example by OH.
A is preferably a radical of the formula xe2x80x94(CH2)nxe2x80x94, in which n is an integer from 2 to 6.
Particularly suitable radicals A are ethylene, n-propylene, iso-propylene or n-butylene. Among these, n-propylene is especially preferred.
R6 and R7 independently of one another are each linear or branched unsubstituted C1-C6alkyl, or C1-C6alkyl which is substituted, for example by OH or C1-C4alkoxy. The alkyl chains can also be interrupted, for example by xe2x80x94Oxe2x80x94.
Preferably, R6 and R7 independently of one another are each unsubstituted C1-C4alkyl, and in an especially preferred embodiment R6 and R7 are identical and are each methyl or ethyl.
A 5-, 6- or 7-membered ring of R6 and R7 together with the N atom joining them is, in particular, a pyrrolidine, piperidine, morpholine or piperazine ring. The piperazine radical can be substituted on the N atom which is not bonded to the alkylene chain, for example by alkyl.
In the dyes of the formula (1), the sulfo group is preferably located in the m- or, in particular, in the p-position relative to the azo group.
Preferred concentrated solutions according to the invention comprise a dye of the formula 
in which
m is 2, 4 or, in particular, 3, and
R6 and R7 are each C1-C2alkyl.
The concentration of the dye can vary within wide limits and is at least 5% by weight, preferably 6 to 15% by weight, in particular 8 to 10% by weight, based on the weight of the concentrated solution.
The alkylcarboxylic acid is, for example, acetic acid, propionic acid, butyric acid or valeric acid. Propionic acid and, in particular, acetic acid are preferred.
Suitable solubilizing agents are, for example, compounds of the following groups:
I) alkali metal or ammonium salts of C1-C4alkylcarboxylic acids,
II) low molecular weight acid amides,
III) low molecular weight lactams or lactones,
IV) alkanolamines or reaction products of ethylene oxide and/or propylene oxide with alkanolamines.
The solubilizing agents of group I) are, in particular, the sodium, potassium, lithium or ammonium salts of acetic acid or propionic acid. Sodium and ammonium acetate are particularly preferred. The solubilizing agents of group I) do not of course have to be employed in the form of the salts mentioned, but can also be prepared in the solutions from the corresponding bases and acids by neutralization.
Low molecular weight acid amides are, in particular, formamide, and especially urea. Suitable solubilizing agents of group III) are, for example, xcex3-butyrolactam or xcex5-caprolactone, but in particular xcex3-butyrolactone, or especially xcex5-caprolactam.
The solubilizing agents of group IV) are, for example, diethanolamine or triethanolamine, but in particular reaction products of 1 to 6 mol of ethylene oxide and/or propylene oxide with 1 mol of diethanolamine or triethanolamine. Particularly preferred compounds are those of the formula 
in which
p is an integer from 1 to 6 and of the substituents R8 and R9, one is hydrogen and the other is hydrogen or methyl.
Preferably, in the compounds of the formula (3), p is 1.
The solubilizing agents of group 1) are preferably present in an amount of 1 to 6% by weight, in particular 1 to 3% by weight, based on the weight of the solution.
The solubilizing agents of groups II), III) and IV) are preferably present in an amount of 3 to 20% by weight, in particular 6 to 15% by weight, based on the weight of the solution.
It is also possible to employ mixtures of solubilizing agents of one group or mixtures of solubilizing agents of different groups, for example mixtures of ammonium acetate and urea.
The C1-C4alkylcarboxylic acid is preferably employed in an amount of 3 to 20% by weight, in particular 6 to 15% by weight, based on the weight of the solution.
Further additives which can be present in the concentrated solutions according to the invention are organic solvents, for example dimethylsulfoxide, N-methylpyrrolidone, ethylene glycol, propylene glycol or glycerol, and boric acid.
The concentrated aqueous solutions of group A) according to the invention can be prepared, for example, by filtering the dye solution obtained during preparation of the dye, subsequently adding the C1-C4alkylcarboxylic acid, the solubilizing agent and, if appropriate, further additives, while stirring, and finally adjusting the desired concentration with water.
The concentrated aqueous solutions according to the invention of group B) comprise no solubilizing agents and may therefore comprise only little alkali metal halide, since otherwise highly viscous solutions or those having an inadequate storage stability are obtained. As a result of the synthesis of the dyes of the formula (1) which is usually carried out by reaction of cyanuric chloride with the corresponding amines at an alkaline pH, however, the dye solutions usually comprise considerable amounts of alkali metal halide and must therefore be brought to an alkali metal halide content of less than 0. 1% by weight, based on the total weight of the solution, by a suitable process.
This is achieved in a manner known per se, for example by reverse osmosis, ultrafiltration or dialysis. Such desalination processes are known, for example from EP-A0059782. The membranes used in these processes are also known, for example from EP-A0061424.
The process conditions of this desalination are chosen such that dye solutions which comprise less than 0.1% by weight, preferably less than 0.07% by weight, based on the total weight of the solution, of alkali metal halides are obtained.
Alkali metal halide in this Application is to be understood as meaning the fluoride, chloride, bromide or iodide of lithium, sodium or potassium.
The concentrated aqueous solutions according to the invention of group B) can thus be prepared, for example, by filtering and desalinating the dye solution obtained during preparation of the dye, subsequently adding the C1-C4alkylcarboxylic acid and, if appropriate, further additives, while stirring, and finally adjusting the desired concentration with water.
The concentrated aqueous dye solutions according to the invention are stable for several weeks at storage temperatures of between 60xc2x0 and xe2x88x9220xc2x0 C. and are suitable for dyeing paper, an which they produce attractive red colour shades of high light-fastness with or without the use of a sizing agent and/or filler.
The dye solutions can be used by all the processes customary for substantive dyes in the paper industry, in particular in pulp and in surface dyeing of paper for sized and nonsized grades, starting from bleached or unbleached cellulose of varying origin, such as softwood or hardwood sulfite and/or sulfate cellulose, mechanical wood pulp or mixtures thereof with cellulose.
The dyes of the formulae (1) and (2) are known, for example from JP-A-075924, or can be obtained analogously to the preparation procedure described therein.
In the following examples, parts are parts by weight and the temperatures are stated in degrees Celsius.